RESUMEN

A convenient and simple three-step pathway to the new family of CF(2)CF(2)S-bridged alkanes and CF(2)S-, CF(2)O-bridged alkenes and alkynes was elaborated by using catalytic olefination reaction as a key step of the synthetic sequence. The obtained compounds revealed attractive liquid crystalline characteristics.

RESUMEN

The reaction of beta-halogeno-beta-polyfluoromethylstyrenes with N,N- or N,O-binucleophiles leads to unexpected fragmentation products (imidazolines) or to heterocyclization giving CF(3)-substituted imidazolidines (N,N-) and oxazolidines (N,O-) depending on aryl substituent. The scope and the reaction mechanism are discussed.

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RESUMEN

The results of a high-resolution ambient STM study of 'sulflower' (octathio[8]circulene) and 'selenosulflower' (sym-tetraselena-tetrathio[8]circulene) molecules, immobilized in a hydrogen-bonded matrix of trimesic acid (TMA) at the solid-liquid interface, are compared with the STM and X-ray structure of separate host and guest 2D and 3D crystals, respectively.

RESUMEN

We report a fabrication of field-effect transistors using the new organic semiconductors octathio[8]circulene and tetrathiotetraseleno[8]circulene . The maximum hole mobility of 9 x 10(-3) cm(2) V(-1) s(-1) is, most likely, limited by one-dimensional growth of and in thin films.

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RESUMEN

Sublimation of sulflower, octathio[8]circulene C 16S 8 ( 1), on heating under high vacuum ( approximately 10 (-5) Torr) leads to successive formation of two modifications: a white film ( 1W) and a red polycrystalline solid ( 1R). When kept at room temperature for several weeks, 1W spontaneously turns pink, reflecting the monotropic phase transition 1W --> 1R. The accurate molecular and crystal structure of 1R has been studied using low-temperature (100 K) high-resolution single crystal X-ray analysis. The C 16S 8 molecule in crystal is strictly planar with nearly equalized bonds of each type (C-C, C-S, and CC). The point symmetry group of the free molecule is D 8 h , and the crystal space group is P2 1/ n. These data allowed group-theoretical analysis of vibrational normal modes to be accomplished. Investigation of the charge density distribution of 1R including Bader's AIM approach has revealed rather strong intermolecular S...S, S...C, and C...C interactions of charge transfer and pi-stacking types with overall lattice energy of 28.5 kcal/mol. The charge transfer due to the S...S interactions is the reason for the red coloration of 1R. The latter is reflected by its UV-vis spectrum exhibiting absorption bands in the visible region which are absent from that of 1W. Both modifications were studied comparatively by vibrational (Raman, IR) and electronic spectroscopies as well as XRD powder diffraction. All the results obtained are fully consistent and show that 1W is much less ordered than 1R with significantly weakened intermolecular interactions. Rationalizing of these results has led to an idea that 1W could be soluble, in contrast to 1R. Indeed, 1W appeared soluble in common solvents; this finding opens the way to the study of the chemistry of 1 and investigation of its electrooptical properties.

RESUMEN

The first example of a diastereoselective thio-Ugi reaction with chiral alpha-methylbenzylamine is described. The reaction results in formation of two diastereomers of thioamides, the major of which was isolated. We have found that under similar conditions stereochemical results of the thio-Ugi reaction are opposite to stereochemical results of the Ugi reaction. Several chiral thioamides were synthesized. The reaction of thioamides with ammonia results in substituted amidines, which can be cyclized to imidazole derivatives in aqueous HCl. The synthesis of chiral imidazole derivatives was elaborated. Using certain approaches, both isomers of a key synthon in the synthesis of SB203386 (an orally bioactive HIV-1 protease inhibitor) were prepared. The scope, limitations, and stereochemistry of the approach are discussed.

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RESUMEN

Herein, we study the conjugation properties of three different thienoacenes, each of which has three or four fused thiophene rings, by means of Fourier transform Raman spectroscopy. The B3LYP/6-31G** vibrational analysis of all of the collected spectroscopic data evidences that the selective enhancement of a limited number of Raman scatterings is related to the occurrence in the three thienoacenes of a vibronic coupling between the lowest unoccupied frontier molecular orbital (LUMO) and some Raman-active skeletal nu(C==C) stretching modes of 1600-1300 cm(-1).

RESUMEN

The synthesis, structure, and electronic properties of a novel cross-conjugated 10H-bisthienodithiocin-10-dicyanoethylene are reported. The X-ray single-crystal structure of the compound reveals a nonplanar conformation. The FT-IR and FT-Raman spectra of the compound show a great resemblance, which is a spectroscopic observation common to many push-pull systems. The UV-vis spectrum in CHCl3 displays a strong absorption at 370 nm accompanied by a shoulder at 430 nm so that the optical gap is 2.88 eV. On the other hand, the electrochemical gap amounts to 2.38 V. DFT and TDDFT quantum chemical calculations, at the B3LYP/6-31G** level, have been also performed to (i) determine the minimum-energy molecular structure, (ii) gain knowledge about the equilibrium atomic charges distribution, the topologies, and absolute energies of the frontier molecular orbitals around the gap and about the molecular vibrations which give rise to the most outstanding Raman bands experimentally evidenced, and (iii) to analyze the nature of the vertical one-electron excitations associated to the strongest UV-vis absorptions.

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RESUMEN

[reaction: see text] A new convenient method for the construction of thiophene-annulated thieno[2,3-b]thiophenes has been proposed. The key step of the method is ring closure of 10H-bisthienodithiocin-10-one by strong bases. The syntheses of two previously unknown annulated oligothiophenes, thieno[2,3-b]thieno[3',2':4,5]thieno[3,2-d]thiophene (1a) and thieno[3,2-b]thieno[2',3':4,5]thieno[3,2-d]thiophene (1b), have been described to illustrate the success of the method.

RESUMEN

A new simple and efficient one pot transformation of various aliphatic carbonyl compounds to the corresponding dibromoalkenes is described. A wide range of hydrazones of aldehydes and ketones, prepared in situ, were easily converted into dibromoalkenes by treatment with carbon tetrabromide in the presence of CuCl. The reaction proceeds under mild conditions to give the target products in good to high yields.

RESUMEN

The reactions of alpha,beta-unsaturated amide/triflic anhydride complexes (generated in situ from the corresponding amides and triflic anhydride) with dithiophenes and dithienylmethanes proceed as tandem alkylation-Vilsmeier-Haack acylation to form dithieno- and dibenzothieno-fused cycloheptanones and cyclooctanones in moderate to good yields. The reactions of 2-bromo-N,N-dimethylacrylamide/triflic anhydride complex allow preparation of tropones in a simple one-pot procedure. The reaction of 2,2-dibenzothienylmethane with dimethylacrylamide/triflic anhydride complex proceeds unusually to afford dimethylaminonaphthalene in addition to the predictable fused cyclooctanone.

RESUMEN

The reaction of dimethyl sulfide with triflic anhydride leads to the formation of the corresponding dimethyl(trifluoromethanesulfonyl)sulfonium salt. The latter can be used in the mild oxidation of primary and secondary alcohols including unsaturated and natural ones to the corresponding carbonyl compounds in 34-75% yield. The reaction of various sulfides with triflic anhydride was studied. It was found that the reactions give rise to the corresponding dialkyl(trifluoromethanesulfonyl)sulfonium salts. Succeeding treatment with water leads to the formation of sulfoxides in 25-73% yield. Formation of sulfones does not proceed.